Cable TV networks are well-known and have been used for years to distribute RF signals to TV sets over coaxial cable. Traditionally, this has been a “broadcast” type network for one direction RF transmission. This traditional network is now being converted into a bidirectional network and, at the same time, the data bandwidth is being increased as much as possible. Coupled with this is the requirement that the power be delivered through the cable and that digital data be added/removed from the RF transmission, all without reducing the transmission quality of the RF signal to the TV or other connected devices. This is a lot to ask of an interface circuit, particularly where low cost and low radiation susceptibility are important.
Traditionally, the RF coaxial cable terminates at the TV set. Now it is required to insert a junction box into the cable at some point for each terminating location so as to be able to remove the power and add/remove other signals from the cables.
One problem that needs to be solved is to have minimum RF insertion loss when the junction box is inserted into the existing RF cable. In addition, the return loss of both connectors (the input connection and the connection to the TV set) must be greater than 15 dB. Also, the input power must be removed. In terms of safety, the box must have the ability to withstand lightening which is defined as microsecond spikes with an 80 microsecond half-decay point. The voltage spike levels can reach 6000 volts: Line crosses, when high voltage, such as 600 VAC, can get on RF center conductor, must be handled. Also, there must be some method of suspending service by remote signals applied to the RF line. In addition, because of the power delivery aspect, UL Creepage and Clearance must be met. All of this must be activated while still maintaining low cost manufacturing costs which equates to a low cost manufacturing process.
Typically, what has been done is that there have been different circuits to solve each of those problems. Thus, there are in-line power tap circuits and tuners on printed and circuit boards with connectors thereon which can cut off the RF signal when desired. Usually, these solutions have been add-ons to the tuner and are typically external to the tuner board. To date, with each add-on handling only a subset of the problems. Today there does not exist an integrated tuner solution to the problems discussed above.